This invention relates to EL(electroluminescent) panels that are particularly suited for use as illuminated instrument panels for aircraft, automotive vehicles and the like. This invention relates also to a novel method of producing such panels.
It is customary to illuminate automotive dashboard and aircraft panels primarily to backlight any nomenclature on the faces thereof, and to outline their various instruments and gages. U.S. Pat. Nos. 3,545,110 and 3,621,595, for example, disclose a method of manufacturing instrument panels which utilize an EL (electroluminescent) light source for illuminating selected areas on the face of the panel.
As taught by these two patents, a sheet of light transmissive plastic material is vacuum formed over a die plate, which forms in the sheet a plurality of recesses for accommodating a variety of instruments. A plurality of EL lamps are then mounted in the back of the formed sheet with their illuminable surfaces surrounding the instrument recesses and facing the inside of the formed sheet. The back of the sheet, which is surrounded by a flange, is then filled with a potting compound, which covers the EL lamps and secures them against movement relative to the formed sheet. Thereafter openings are formed in the bottoms of the recesses and instruments are secured in the recesses with their faces fronting on the openings to be surrounded by the EL lamps that are embedded in the potted sheet. This completes the instrument panel, which can then be secured in place in an aircraft or automotive vehicle, after which the leads or the EL lamps are connected to a power supply selectively to be illuminated thereby.
Among the major advantages of EL panels of the type described is that they can be readily shaped into plane or curved surfaces; and they also can utilize a relatively low power source for energizing the various EL lamps in the panel. Among the disadvantages of these prior art panels, however, is that the potting material, which is flowed into the back of the panel to secure the EL lamps in place, adds considerably to the overall weight and cost of the panel. It is therefore most desirable to be able to reduce the quantity of potting material employed, but without altering the quality of the finished instrument panel. Moreover, because of the differences in the rates of contraction and expansion of the plastic sheet and the potting material, respectively, the possibility of distortion of the finished panel in response to extreme temperature changes, such as during curing of the potting material, is reduced as the quantity of potting material is reduced.
Heretofore efforts have been made to reduce the overall weight of panels of the type described by using a milling machine for hogging out portions of the potting material at the rear of the panel. The disadvantage of this procedure, of course, is that it adds considerably to the overall cost of the panel, and does not solve the problem of panel distortion which may occur during curing.
It is an object of this invention, therefore, to provide an improved EL panel of the type described which utilizes substantially less potting material than prior such panels, and therefore is substantially lighter in weight and less expensive to manufacture.
Another object of this invention is to provide an improved method for minimizing the amount of potting material required to be used during the fabrication of the EL panels.
Other objects of the invention will be apparent hereinafter from the specification and from the recital of the appended claims, particularly when read in conjunction with the accompanying drawings: